145. Solving a chemistry problem

70. A portion of the alloy weighing 0.2500 g was dissolved in a mixture of acids and transferred to a volumetric flask with a capacity of 500.00 ml. The atomic absorption of manganese at 279.5 nm is equal to 25 divisions of the scale. To construct the calibration graph, a series of standard solutions was prepared with a concentration of 2.0 4.0 6.0 8.0 and 10.0 μg Mn in 1.00 ml. For them, the atomic absorption for each standard solution was measured, respectively: 10 20 30 40 and 50 divisions of the scale. Determine the mass fraction of manganese in the alloy.